The present invention relates to an optical waveguide module with a fiber coupling composed of a supporting substrate having at least one integrated optical waveguide whose ends each are optically coupled, on each of two sides of the supporting substrate, to one end of a respective optical fiber with each fiber being fixed in the groove of a respective holder which is attached to the substrate.
Such modules are generally used as sensors and for optical communication. They consist of planar structures in which a substrate with an integrated optical circuit is implemented, for example, as a phase modulator, beam splitter, Mach-Zehnder interferometer, etc.
In an article entitled "Fiber Attachment for Guided Wave Devices", JOURNAL OF LIGHTWAVE TECHNOLOGY, Vol. 6, No. 6, June 1988, pages 862 to 871, waveguide modules with different fiber attachments and the difficulties encountered in their manufacture are described. For individual fiber attachment, the thickness of the substrate is increased by bonding a fillet to the substrate and butt-joining the fiber end to the outside of the substrate and fillet with adhesive. For increased stability, the fiber end may previously be fixed in a tubule or a suitable jewel with adhesive. However, this method is not suitable for attaching polarization-maintaining fibers because the substrate is made of lithium niobate, the tubule of metal, and the fiber end of quartz glass, and these materials have different coefficients of expansion, so that in case of temperature variations, the polarization of the light waves in the optical fiber would be adversely affected or destroyed.
In the example described in the article for the attachment of an array of polarization-maintaining optical fibers, the fiber ends are fixed between a grooved silicon chip and a glass plate covering the grooves, and the arrangement is bonded to the outside of the substrate, which is again strenghtened in the area of connection by means of a fillet. Such an array attachment is relatively expensive. The groove in the silicon chip are formed by anisotropic etching, which is relatively time-consuming. In addition, silicon, because of its crystalline structure, is rather brittle, so that special care must be taken in handling it during manufacture, and must be strenghtened by the glass plate to increase stability. Array attachment requires very good core-cladding concentricity. Polarization-maintaining fibers for wavelengths &lt;1 .mu.m, in particular, do not meet these requirements.